1. Field of the Invention
The present invention relates to a unitary sealed tactile effect key, particularly for a keyboard of the type comprising:
a support plate with recesses each adapted for receiving switch elements, PA1 a printed circuit for electric connection of said switch, this printed circuit possibly forming said support plate, PA1 a molded spacer integral with the support plate and comprising, between dividing walls, a housing having at least one upper opening in which is housed a key-pusher assembly mounted for sliding in said housing and in mechanical connection with the switch, PA1 deformable means associated with said key-pusher-switch assembly for giving the user a tactile feeling. PA1 a support having a recess adapted for receiving a switch element which can be actuated under the effect of a pressure exceeding a given force threshold, PA1 a resilient membrane integral with the support which forms a cap closing the recess, this membrane having, on the side opposite the recess and substantially coaxially therewith, a resiliently deformable stud which serves as pusher, PA1 a key associated with the pusher, on which a force may be exerted for actuating the switch element. PA1 a pre-travel phase during which the resistant force exerted by the key on the finger of the user increases progressively until the force applied to the key reaches the force threshold, PA1 an active phase during which the travel of the key is practically zero and actuation of the switch is due to partial expansion of the material of the stud, the resistant force decreasing suddenly while producing a feeling of release, PA1 an over-travel phase at the beginning of which the resistant force increases again progressively then rises suddenly when the conformations of the key limiting the expansion of the stud come into action.
2. Description of the Prior Art
A keyboard with keys of this type is known, in which said deformable means are formed by a flexible membrane common to all the keys and placed above the support plate for protecting the recesses and ensuring the resilient return of the keys to which said membrane is connected by nipping with an element of the switch.
The major drawback of this type of keyboard resides in the fact that the flexible membrane as well as the support plate are formed with a multiplicity of openings, in number equal to the number of switches equipping the keyboard. Thus, after a certain number of operations, overstretching of the material occurs which, associated with ageing in time thereof, no longer allows the membrane to provide sealing of the unit. In addition, the tactile effect obtained in this type of known keyboard is not controlled. In fact, it is due to the resistance of the membrane alone, which is deformed laterally under the effect of an axial thrust on the key, to which is added that of a spring element of the switch until the latter rocks.
Such rocking allows the operator to feel by tactile effect that his operation has been taken into account. On the other hand, beyond such rocking, a certain over-travel producing a certain comfort in use is only obtained by crushing of the membrane in a limited and uncontrolled way.
From the patent DE-A-2 828 435, it has also been proposed to insert a damping element between the key and the element actuating the switch. However, this solution, which only shifts the response curve of the actuating element of the switch, does not allow the desired result to be obtained.